Most electronic devices, including computers and computerized devices, are supplied electrical power by a remote alternating current (AC) generator, and typically share a power line with a large number of other devices. Community power supplies and transmission systems are subject to disturbances (variations or interruptions) which can detrimentally affect the operation of the devices connected thereto. The present invention is directed toward methods and apparatus for accommodating power disturbances, and particularly momentary power outages.
Community or shared power lines can suffer from a wide assortment of long-term and short-term or transient problems. For AC power systems, there can be variations in the frequency and/or amplitude. Though the former is usually acceptably stable, surges (fairly long-term amplitude variations) and spikes (short-term variations) can occur on a regular basis. Unfortunately, there may even be periods where power is lost altogether. Such problems can be attributed to the power generator or to the transmission system. Environmental conditions e.g. lightning storms, can cause power surges, spikes and/or outages. Further, problems can be caused by the end users themselves by making sudden substantial demands on the power system, by, for example, activating or deactivating large motors, relays, and the like.
Most spikes and surges can be readily accommodated through the use of fuses, circuit breakers and filters of various types. Fuses and circuit breakers are designed to handle over-current conditions by interrupting power to the load device, and must be generally manually reset or replaced. Filters, on the other hand, prevent disturbances from reaching the load devlce but do not "blow" or "trlp", and thus do not need to be manually re-established. One type of filter uses metal oxide varistors to regulate or clamp the AC voltage. Traditional capacitors and RC networks have also been used to filter transients. Some electronic devices are supplied with power back-up systems which are designed to maintain a continuous supply of power to the device in the event of a power outage. Such back-up systems can be quite expensive. Thus, at least for some electronic devices, momentary power outages pose a significant problem. As discussed below, computer devices are particularly sensitive to momentary power outages, and the present invention addresses this problem.
While all electronic devices can be detrimentally affected by power disturbances to some degree, computer devices (computers and devices and systems including computers) are particularly sensitive to power supply problems. Storage or memory components within such devices are typically volatile. Also, timing is critical in computer devices. Finally, given the tens if not hundreds of thousands of logic gates in a typical computer, and given the critical nature of the data and computations handled by such devices, any power irregularities are undesirable. Thus, although the present invention is applicable to a wide variety of electronic devices, for the sake of brevity the following discussion will focus on computers and computerized systems and devices.
Computers and computerized devices and systems are affected by power disturbances (e.g., momentary power outages) in several ways, depending on, among other things, the sophistication of the computer's internal power supply; the presence or absence of a power back-up system; and the nature of the disturbance. Random access memory (RAM) is particularly sensitive to power disturbances, potentially responding by corrupting the logic and/or data contained within the machine. This "corruption" can result from loss of or change in the information stored in RAM. Another problem which can result is a complete lock-up or freeze of the machine wherein the processor is incapable of executing instructions.
Data or logic corruption and/or machine freeze-up are particularly troublesome when the computer or computerized device is operated in an unattended mode. This is because there is no machine operator present to detect and correct such problems. Since most computers are capable of restarting or rebooting themselves in response to a fairly long-term (e.g. five seconds or more) power outage, but are incapable of handling a shorter term power outages, unattended operation is unreliable when momentary power outages are anticipated.
An example of an unattended computerized system is an irrigation system wherein a microcomputer is used to control a large number of valves, pumps and the like. If power to the microcomputer is interrupted for less than about 0.5 second, capacitors within the computer's own power supply circuit are capable of "smoothing" the loss of power and preventing any loss of data or freeze-up. Also, if the power loss lasts for a relatively long period of time (e.g.. five or six seconds) the computer will simply restart itself or "reboot" once power is resumed. The computer then simply determines the status of matters by reading a clock, polling humidity sensors and the like, and then activates the electromechanical devices as necessary. By contrast, if the power loss lasts for more than about 0.5 second. but less than perhaps five or six seconds, the results can be disastrous: the control computer can freeze or lock-up, or have its program or data corrupted, and thus be rendered incapable of properly controlling the valves and pumps of the system.
Short-term power loss to computer devices can be problematical even in attended settings. It is possible that such a power loss could cause a corruption in the data or logic which would not be detected by the operator. It would thus be advantageous, even in some attended operations, to completely remove power from the computer for a period of time to allow the machine to reboot with a valid set of data and instructions. Although this might require the operator to reenter data, it might be preferable in some circumstances where the data is quite critical and the reentry time ls not too onerous.
The present invention addresses the problems discussed above. In particular, the invention addresses the problem of short-term power disturbances, e.g. short-term power loss, in the AC electrical supply for computer devices.